Attachment optical system and projection display system

ABSTRACT

An attachment optical system is detachably attached to a magnification side of a projection optical system of a projection display device, and projects light emitted from the projection optical system on an imaging plane different from a magnification side imaging plane of the projection optical system. The attachment optical system includes an optical element having a second optical axis as an extension of a first optical axis of the projection optical system. The optical element has a plane of incidence on the second optical axis, a first reflecting surface that reflects light emitted from the plane of incidence, a second reflecting surface that reflects light reflected by the first reflecting surface, and an exit surface that transmits light reflected by the second reflecting surface. The first reflecting surface and the exit surface are continuous in an axial area where light passes the second optical axis and the first optical axis.

The present application is based on, and claims priority from JPApplication Serial Number 2021-060379, filed Mar. 31, 2021, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to an attachment optical system and aprojection display system.

2. Related Art

An attachment optical system to detachably be attached to a projectionoptical system of a projector is described in JP-A-2011-257630 Document1). The attachment optical system in Document 1 is provided with ananterior group constituted by two reflecting surfaces and twotransmissive surfaces rotationally symmetric around a central axis, anda posterior group which is rotationally symmetric around the centralaxis and has positive power. The anterior group is a certain opticalelement formed of a transparent medium. The anterior group isconstituted by a first transmissive surface having positive power ofentering the anterior group from afar, a first reflecting surface whichis disposed at a posterior group side across the central axis from thefirst transmissive surface, and has positive power, a second reflectingsurface which is disposed at the same side as the first reflectingsurface, and is disposed at a longer distance from the posterior groupthan the first reflecting surface, and a second transmissive surfacewhich is disposed at the extreme posterior group side, and has negativepower in the order in which the light beam proceeds.

The attachment optical system is attached to the projector so that thecentral axis of the attachment optical system coincides with the opticalaxis of the projection optical system. In the state in which theattachment optical system is attached to the projector, the firsttransmissive surface is located on an extension of the optical axis ofthe projection optical system. The first reflecting surface and thesecond reflecting surface are located at one side of the optical axis ofthe projection optical system. The second transmissive surface islocated at the other side of the first reflecting surface and the secondreflecting surface across the optical axis of the projection opticalsystem, and is at a distance from the extension of the optical axis ofthe projection optical system. Therefore, in Document 1, projectionlight which is emitted from the projector, and proceeds toward a screenvia the attachment optical system is emitted toward a direction whichdoes not overlap the extension of the optical axis of the projectionoptical system of the projector. As a result, an enlarged image of aprojection image to be projected via the projection optical system andthe attachment optical system is formed on an imaging plane having acircular arc shape extending in a circumferential direction around theoptical axis of the projection optical system.

There is a demand of making projection light proceeding toward thescreen via the attachment optical system reach the extension of theoptical axis of the projection optical system of the projector when theattachment optical system is attached to the projection optical systemof the projector.

SUMMARY

In view of the problems described above, an attachment optical systemaccording to the present disclosure is detachably attached to amagnification side of a projection optical system provided to aprojection display device, and projects projection light emitted fromthe projection optical system on an imaging plane different from amagnification side imaging plane of the projection optical system. Theattachment optical system is provided with an optical element having asecond optical axis arranged on an extension of a first optical axis ofthe projection optical system. The optical element has a plane ofincidence arranged on the second optical axis, a first, reflectingsurface configured to reflect light emitted from the plane of incidence,a second reflecting surface configured to reflect light reflected by thefirst reflecting surface, and an exit surface configured to transmitlight reflected by the second reflecting surface. The first reflectingsurface and the exit surface are continuous in an axial area where lightpasses the second optical axis and the first optical axis.

Further, a projection display system according to the present disclosureincludes the attachment optical system described above, and a projectiondisplay device having a projection optical system. The attachmentoptical system is detachably attached to the projection optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a ray diagram schematically showing the whole of the projectorto which the attachment optical system according to Practical Example 1can be attached.

FIG. 2 is a ray diagram of a projection optical system of the projector.

FIG. 3 is a ray diagram schematically showing the whole of a projectorsystem according to Practical Example 1.

FIG. 4 is a ray diagram of the projection optical system of theprojector and the attachment optical system according to PracticalExample 1.

FIG. 5 is a configuration diagram of the attachment optical systemaccording to Practical Example 1.

FIG. 6 is a diagram showing an MTF at a magnification side of theprojector system according to Practical Example 1.

FIG. 7 is a ray diagram schematically showing the whole of a projectorsystem according to Practical Example 2,

FIG. 8 is a ray diagram of the projection optical system of theprojector and an attachment optical system according to PracticalExample 2.

FIG. 9 is a configuration diagram of the attachment optical systemaccording to Practical Example 2.

FIG. 10 is a diagram showing an MTF at a magnification side of theprojector system according to Practical Example 2.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

A projector system as an embodiment of a projection display systemaccording to the present disclosure will hereinafter be described indetail with reference to the drawings.

Practical Example 1

FIG. 1 is a ray diagram schematically showing the whole of the projector1 to which the attachment optical system 10A can be attached. FIG. 2 isa ray diagram of a projection optical system 3 of the projector 1. FIG.3 is a ray diagram schematically showing the whole of a projector system100A. FIG. 4 is a is a ray diagram of the projection optical system 3 ofthe projector 1 and the attachment optical system 10A. FIG. 5 is aconfiguration diagram of the attachment optical system 10A. In FIG. 1through FIG. 5, a light flux emitted from the projector 1 and theprojector system 100A is schematically shown using light fluxes F0through F10. The light flux F0 is a light flux emitted from theprojector 1 and the projector system 100A, and then passes on a firstoptical axis N of the projection optical system 3. The light flux F10 isa light flux which reaches the position where the image height is thehighest. The light fluxes F1 through F9 are each a light flux whichreaches an intermediate position between the positions of the light fluxF0 and the light flux F10.

The projector system 100A according to the present example is providedwith the projector 1 as a projection display device, and the attachmentoptical system 10A detachably attached to the magnification side of theprojection optical system 3 provided to the projector 1. Hereinafter,the projector 1 is described first, and then, the attachment opticalsystem 10A is described.

As shown in FIG. 1, the projector 1 is provided with a light modulationelement 2 for modulating light from a light source to form a projectionimage, a projection optical system 3 for projecting the projection imageformed by the light modulation element 2 in an enlarged manner, and achassis 4 for supporting the projection optical system 3. The lightmodulation element 2 is housed inside the chassis 4.

As shown in FIG. 2, the projection optical system 3 is a refractingoptical system provided with a plurality of lenses. The light,modulation element 2 is a liquid crystal panel. The light modulationelement 2 is disposed on a demagnification side imaging plane of theprojection optical system 3. The demagnification side imaging plane isperpendicular to the first optical axis N of the projection opticalsystem 3. The light modulation element 2 forms the projection imagebelow the first optical axis N. As shewn in FIG. 1, first projectionlight B1 emitted from the projection optical system 3 spreadshorizontally and upward with respect to the first optical axis N. Asshewn in FIG. 1, when using the projector 1 alone, a screen S1 isdisposed on the magnification side imaging plane of the projectionoptical system 3. The magnification side imaging plane is perpendicularto the first optical axis N of the projection optical system 3.

Then, as shown in FIG. 3, the attachment optical system 10A is attachedto a tip portion of the projection optical system 3 of the projector 1.In the present example. in order to conform a spreading direction of theprojection light between before and after the attachment of theattachment optical system 10A to the projector 1, the attachment opticalsystem 10A is attached to the projection optical system 3 after flippingthe projector 1. Therefore, at the time point when the attachmentoptical system 10A is attached, the light modulation element 2 of theprojector 1 forms the projection image above the first optical axis N ofthe projection optical system 3 as shown in FIG. 4. The first projectionlight B1 of the projector 1 spreads horizontally and downward withrespect to the first optical axis N.

The attachment optical system 10A is provided with an anterior group 11and a posterior group 12 (lens groups). In the present example, theanterior group 11 is formed of a single optical element 21. Theposterior group is formed of a single positive lens 31 (a first lens).The positive lens 31 is disposed at the projection optical system 3 sideof the optical element 21, and has positive power. The posterior group12 is located between the anterior group 11 and the projection opticalsystem 3. A second optical axis M of the attachment optical system 10Ais located on an extension of the first optical axis N of the projectionoptical system 3. The second optical axis M is an optical axis of theoptical element 21, and at the same time, an optical axis of thepositive lens 31.

An imaging plane ox the projector system 100A, namely an imaging planeof the projection optical system 3 and the attachment optical system10A, has a shape of an inside surface of a spherical portion obtained bydividing a sphere. In the present example, the imaging plane of theattachment optical system 10A has a shape of an inside surface of aspherical portion obtained by dividing a sphere into four equal parts.The shape of the imaging plane of the projector system 100A is differentfrom the shape of the magnification side imaging plane of the projectionoptical system 3. In ocher words, the optical system of the projectorsystem 100A constituted by the projection optical system 3 and theattachment optical system 10A is capable of projecting the projectionimage on a imaging plane different from that of the projection opticalsystem 3. when using the projector system 100A, a screen S2 having ashape of the inside surface of the spherical portion obtained bydividing a sphere into four equal parts is disposed on the imaging planeof the projection optical system 3 and the attachment optical system10A. Second projection light B2 emitted from the attachment opticalsystem: 10A spreads horizontally and upward with respect to the secondoptical axis M.

In the following description, three axes perpendicular to each other aredefined as an X axis, a Y axis, and a Z axis for the sake ofconvenience. Further, an optical axis direction along the first opticalaxis N of the projection optical system 3 and the second optical, axis Mof the attachment optical system 10A is defined as a Z direction. Awidth direction of the screen 32 as the imaging plane of the projectionoptical system 3 and the attachment optical system 10A is defined as anX-axis direction, and a vertical direction of the screen S2 is definedas a Y direction. Further, in the Z direction, a side at which theprojection optical system 3 is located is defined as a Z1 direction, anda side at which the attachment optical system 10A is located is definedas a 22 direction. Further, a lower side and a downward direction aredefined as a Y1 direction, and an upper side and a upward direction aredefined as a Y2 direction.

Details of Projection Optical System and Attachment Optical System

As shown in FIG. 4, the projection optical system 3 is provided withlenses L1 through L11 in this order from the demagnification side towardthe magnification side. The light modulation element 2 is disposed onthe demagnification side imaging plane of the projection optical system3. The light modulation element 2 forms the projection image at the Y2direction side of the first optical axis N of the projection opticalsystem 3. A prism 5 is disposed between the light modulation element 2and the projection optical system 3. The first projection right 31 fromthe projection optical system 3 is emitted in the Y1 direction towardthe Z2 direction from the lens L11.

The attachment optical system 10A is provided with the posterior group12 and the anterior group 11 arranged from the projection optical system3 side. In the present example, the posterior group 12 is the singlepositive lens 31 (the first lens), and the anterior group 11 is thesingle optical element 21. The optical element 21 is formed of atransparent optical member partially provided with reflective coating.The optical element 21 is provided with a plane of incidence 41 whichtransmits light from the positive lens 31, a first reflecting surface 42which reflects the light transmitted through the plane of incidence 41,a second reflecting surface 43 which reflects the light from the firstreflecting surface 42, and an exit surface 44 which transmits the lightfrom the second reflecting surface 43. In other words, the opticalelement 21 has the plane of incidence 41, the first reflecting surface42 which reflects the light emitted from the plane of incidence 41, thesecond reflecting surface 43 which reflects the light reflected by thefirst reflecting surface 42, and the exit surface 44 which transmits thelight reflected by the second reflecting surface 43. The plane ofincidence 41, the first reflecting surface 42, the second reflectingsurface 43, and the exit surface 44 are each provided with the shaperotationally symmetric around the second optical axis M.

The plane of incidence 41 is located on the second optical axis M. Theplane of incidence 41 is provided with a concave shape concaved towardthe 22 direction. In other words, the plane of incidence 41 has theconcave shape concaved toward the 22 direction (a second direction)opposite to the Z1 direction (a first direction) in which the projectionoptical system 3 is located with respect to the optical element 21 in anoptical axis direction along the second optical axis M. The firstreflecting surface 42 is located at the 22 direction side of the planeof incidence 41. Further, the first reflecting surface 42 is disposed atthe Y1 direction side of the second optical axis M. The first reflectingsurface 42 is provided with a convex shape con vexed toward the Z1direction The second reflecting surface 43 is located at the Z1direction side of the first reflecting surface 42. Further, the secondreflecting surface 43 is disposed at the Y1 direction side of the secondoptical axis M similarly to the first reflecting surface 42. The secondreflecting surface 43 is provided with a concave shape concaved towardthe Z1 direction. The exit surface 44 is located at the Z2 directionside of the second reflecting surface 43. Further, the exit surface 44is disposed at the Y2 direction side of the second optical axis M. Theexit surface 44 is provided with a convex shape convexed toward the Z2direction.

As shown in FIG. 5, the first reflecting surface 42 and the exit,surface 44 are continuous in an axial light flux pass area (the axialarea) 40 of an axial light flux passing the second optical axis M in theY direction. In other words, the axial light flux pass area 40 is a partof the first reflecting surface 42, and at the same time, a part of theexit surface 44. The axial light flux is light passing on the firstoptical axis N and the second optical axis M when the attachment opticalsystem 10A is attached to the projector 1. In other words, the axiallight flux pass area 40 is an area of the optical element 21 where thelight passes the first optical axis N and the second optical axis M.Here, the second optical axis M is a design axis of the optical element21. The axial light flux pass area 40 is an area which is uniquelydefined when designing the optical element 21.

The first reflecting surface 42 is formed by disposing a reflectivecoating layer on an outside surface at the Y2 direction side of theoptical element 21. In the first reflecting surface 42, the portionoverlapping the axial light flux pass area 40 is provided with ahalf-mirror coating layer as the reflective coating layer. Thehalf-mirror coating layer reflects the light crossing the second opticalaxis M toward the Z1 direction, and transmits the light parallel to thesecond optical axis M toward the Z2 direction. Thus, the lightproceeding on the second optical axis M toward the Z2 direction is madeto reach the screen S2.

Further, the first reflecting surface 42, the second reflecting surface43, and the exit surface 44 overlap the plane of incidence 41 in theportion at the side close to the second optical axis M when viewed fromthe Z direction. Here, in the second reflecting surface 43, a firstreflecting part 431 which does not overlap the plane of incidence 41when viewed from the Z direction is formed by disposing a reflectivecoating layer on the outside surface at the Z1 direction side of theoptical element 21. In the second reflecting surface 43, a secondreflecting part. 432 which overlaps the plane of incidence 41 whenviewed from the Z direction is formed by providing a half-mirror coatinglayer which transmits light proceeding toward the 22 direction, andreflects light proceeding toward the Z1 direction as the reflectivecoating layer. It should be noted that in order to dispose thehalf-mirror coating layer, the optical element 21 is constituted by twooptical members, namely a fist member 22 and a second member 23, whereinthe first member 22 is provided with a first outside surface portion 26having a convex shape obtained by transferring a surface shape of thesecond reflecting surface 43 to the outside surface at the Z1 directionside, and the second member 23 is provided with a second outside surfaceportion 27 having a concave shape corresponding to the surface shape orthe second reflecting surface 43 on the outside surface at the Z2direction side. The first member 22 is provided with a reflectivecoating layer in a portion which does not overlap the plane of incidence41 when viewed from the Z direction in the first outside surface portion26, and is provided with a half-mirror coating layer in a portion whichoverlaps the plane of incidence 41 when viewed from the Z direction. Thesecond member 23 is bonded to the first member 22 provided with thereflective coating layer and the half-mirror coating layer from the Z1direction side.

Here, inside the optical element 21, there is formed an intermediateimage 20 which is conjugate with the enlarged image projected on theimaging plane. The intermediate image 20 is also conjugate with theprojection image formed on the demagnification side imaging plane of theprojection optical system 3. In the present example, the intermediateimage 20 is formed between the second reflecting surface 43 and the exitsurface 44.

Lens Data

The numerical aperture of the optical system of the projector system100A constituted by the projection optical system 3 and the attachmentoptical system 10A is 0.291. The lens data of such an optical system isas follows. The surface numbers are provided in sequence from thedemagnification side toward the magnification side. The symbolsrepresent the symbols of the liquid crystal panel, the prism, thelenses, the positive lenses, the first transmissive surface, the firstreflecting surface, the second reflecting surface, the secondtransmissive surface, and the screen. Data of the surface number whichcorresponds to none of the liquid crystal panel, the prism, the lenses,the positive lenses, the first transmissive surface, the firstreflecting surface, the second reflecting surface, the secondtransmissive surface, and the screen is dummy data. The reference symbolR represents a curvature radius. The reference symbol D represents anaxial surface distance. The reference symbol C represents an apertureradius. The units of R, D, and C are millimeter. It should be noted thatthe integer portion of the numerical number shown in the glass materialcolumn represents a value obtained by multiplying the refractive indexby 10 to the sixth power, and the fractional portion thereof representsa value obtained by multiplying the Abbe number by 10 to the secondpower.

Surface Refraction/ Symbol number Shape R D Glass material Reflection C 2 0 Sphere Infinite 0.0010 Refraction 0.0000  5 1 Sphere Infinite29.9441 BSC7_HOYA Refraction 11.0003 2 Sphere Infinite 10.7129Refraction 16.1307 3 Sphere Infinite 1.3170 Refraction 18.9729 L1 4Sphere 100.7098 5.4431 713667.2948 Refraction 19.8463 5 Sphere −102.11540.1500 Refraction 19.9390 L2 6 Sphere 43.1770 6.7243 643138.5620Refraction 19.6870 7 Sphere −398.2098 14.3689 Refraction 19.3609 L3 8Sphere 25.7153 7.0237 487490.7041 Refraction 12.0000 L4 9 Sphere−26.9720 1.0000 755201.2758 Refraction 11.4463 10 Sphere 22.7296 7.0498Refraction 10.1942 L5 11 Aspheric surface −12.8094 2.0000 ‘D-ZF10_K’Refraction 10.2226 12 Aspheric surface −23.2033 0.2735 Refraction11.0391 L6 13 Sphere 33.2589 2.0000 750866.3234 Refraction 12.2908 L7 14Sphere 21.4173 8.9545 487490.7041 Refraction 12.5458 15 Sphere −32.315417.4196 Refraction 13.0465 L8 16 Sphere 457.8045 8.8399 749259.3458Refraction 16.0000 17 Sphere −40.7661 3.8120 Refraction 16.7967 L9 18Sphere 38.3424 9.0000 743972.4485 Refraction 16.2071 19 Sphere 52.10889.2806 Refraction 14.5342 L10 20 Sphere −24.1062 1.0000 504633.6129Refraction 14.0641 21 Sphere 34.0901 3.0358 Refraction 15.2438 L11 22Aspheric surface 35.8481 4.3495 ‘Z-E48R’ Refraction 16.1241 23 Asphericsurface 34.7555 0.2748 Refraction 17.0742 24 Sphere Infinite 2.7542Refraction 15.8710 31 25 Aspheric surface 167.7799 3.4688 ‘Z-330R’Refraction 17.0088 26 Aspheric surface −141.4036 26.5312 Refraction17.2791 41 27 Aspheric surface −247.3414 174.6000 ‘Z-330R’ Refraction25.0955 42 28 Aspheric surface 361.1475 −174.6000 ‘Z-330R’ Reflection64.3156 43 29 Aspheric surface 165.2666 174.6000 ‘Z-330R’ Reflection137.5994 44 30 Aspheric surface −309.4117 10.0000 Refraction 83.0000 31Sphere Infinite 2768.0000 Refraction 1781.1106 S 32 Sphere −2,768.00000.0000 Refraction 2906.3556

Aspheric coefficients are as follows.

Surface number S11 S12 S22 S23 R −12.8094 −23.2033 35.8481 34.7555 K 0 0−0.007858933 −8.273411949 A 1.97478E−04 1.50407E−04 −4.73415E−05 −3.44381E−05  B −8.21635E−07  −7.62802E−07  1.11583E−07 7.17727E−08 C8.67659E−09 5.19871E−09 −1.60660E−10  −1.26152E−10  D −2.93527E−11 −2.35712E−11  1.88569E−13 1.10885E−13 E −3.30348E−14  4.53875E−14−1.74526E−16  −3.42914E−17  F 7.83942E−16 2.61603E−19 −1.13308E−20 Surface number S25 S26 S27 S28 R 167.7799 −141.4036 −247.3414 361.1475 K0 0 −75.66565551 −88.2104460231 A −3.71721E−06  −5.46556E−06 −2.74520E−06  1.55519E−08 B 5.05896E−10 2.74825E−10 6.45342E−103.41360E−11 C 6.79321E−12 5.93487E−12 1.67714E−13 −4.59596E−15  D−2.13955E−15  1.80004E−15 Surface number S29 S30 R 165.2666 −309.4117 K−3.9406340359 −23.8997256640 A 6.69798E−08 −5.56825E−07  B −2.30309E−12 7.93919E−11 C 2.30442E−16 −8.83324E−15  D −5.62829E−21  4.15649E−19

Functions and Advantages

According to the present example, by attaching the attachment opticalsystem 10A to the magnification side of the projection optical system 3of the projector 1, it is possible to project the first projection lightB1 from the projection optical system 3 on the imaging plane differentfrom the magnification side imaging plane of the projection opticalsystem 3. In the present example, the imaging plane of the projectorsystems 100A has the shape of the inside surface of the sphericalportion obtained by dividing a sphere into four equal parts. Therefore,by appreciating the enlarged image inside such an imaging plane, it ispossible for the appreciator to obtain a feeling as if the appreciatorwere surrounded by the picture.

Here, the attachment optical system 10A has the optical element 21provided with the plane of incidence 41, the first reflecting surface 42which reflects the light transmitted through the plane of incidence 41,the second reflecting surface 43 which reflects the light from the firstreflecting surface 42, and the exit surface 44 which transmits the lightfrom the second reflecting surface 43. When the attachment opticalsystem 10A is attached to the projection optical system 3, the secondoptical axis M of the optical element 21 is located on the extension ofthe first optical axis N of the projection optical system 3, and thefirst reflecting surface 42 and the exit surface 44 are continuous inthe axial light flux pass area 40 of the axial light flux passing thesecond optical axis M and the first optical axis N. Therefore, it ispossible to make the second projection light B2 proceeding toward thescreen S2 via the attachment optical system 10A reach the extension ofthe first optical axis N of the projection optical system 3.

Further, the attachment optical system 10A is provided with the plane ofincidence 41 provided with the concave shape concaved toward the Z2direction, the first reflecting surface 42 provided with the convexshape con vexed toward the Z1 direction, the second reflecting surface43 provided with the concave shape concaved toward the Z1 direction, andthe exit surface 44 provided with the convex shape convexed toward theZ2 direction. Since the attachment optical system 10A is provided withthese constituents, it is easy for the attachment optical system 10A toproject the first projection light. B1 from the projection opticalsystem 3 in a more wide-angle manner, and at the same time, image thefirst projection light B1 at short focus length.

Further, in the present example, the single optical element 21 isprovided with the first reflecting surface 42 and the second reflectingsurface 43 as two reflecting surfaces, and the plane of incidence 41 andthe exit surface 44 as two transmissive surfaces. Therefore, it ispossible to suppress the number of optical members in the attachmentoptical system 10A.

Further, in the present, example, the intermediate image 20 which isconjugate with an enlarged image projected on the imaging plane isformed inside the optical element 21. In other words, the opticalelement 21 forms the intermediate image 20 inside, and then images theintermediate image 20 on the imaging plane once again. Therefore, in theattachment optical system 10A, the imaging performance of the projectionimage is improved. Further, when the intermediate image 20 is formedinside the optical element 21, it is easy for the optical element 21 toconvert the projection direction in which the projection image isprojected.

Further, in the present example, the attachment optical system 10A hasthe positive lens 31 disposed at the projection optical system 3 side ofthe optical element 21. Since there is provided such a positive lens 31,it is possible to improve the imaging performance of the attachmentoptical system 10A.

FIG. 6 is a diagram showing an MTF at the magnification side of theprojector system. In FIG. 6, the horizontal axis represents a spatialfrequency, and the vertical axis represents a contrast reproductionrate. As shown in FIG. 6, the projector system 100A in the presentexample has high resolution.

Here, in the present example, the attachment optical system 10A isattached to the projection optical system 3 after flipping the projector1. Thus, the light modulation element 2 of the projector 1 forms theprojection image above the first optical axis N of the projectionoptical system 3 as shown in FIG. 3. The first projection light B1 fromthe projection optical system 3 spreads from the first optical axis Ndownward with respect to the first optical axis N. In contrast, the exitsurface 44 of the attachment optical system 10A is located above thesecond optical axis M, and the first reflecting surface 42 and thesecond reflecting surface 43 are located below the second optical axisM. Thus, the second projection light B2 from the attachment opticalsystem 10A spreads from the second optical axis M upward with respect tothe second optical axis M. In this way, it is possible to conform thespreading direction of the projection light between before and after theattachment of the attachment optical system 10A to the projector 1.

It should be noted that when the projector 1 is provided with, forexample, a shift mechanism for supporting the light modulation element 2so as to be able to move along the Y direction in the demagnificationside imaging plane of the projection optical system 3, it is possible toattach the attachment optical system 10A to the projection opticalsystem 3 without flipping the projector 1. In this case, it is assumedthat the light modulation element 2 is moved by the shift mechanismalone a direction perpendicular to the first optical axis N instead offlipping the projector 1 to form the projection image above the firstoptical axis N. Thus, the first projection light. B1 emitted from theprojection optical system 3 spreads from the first optical axis Nhorizontally and downward with respect to the first optical axis N.Therefore, by locating the exit surface 44 above the second optical axisM, and locating the first reflecting surface 42 and the secondreflecting surface 43 below the second optical axis M when attaching theattachment optical system 10A to the projection optical system 3, thesecond projection light B2 emitted from the attachment optical system10A spreads from the second optical axis M upward with respect to thesecond optical axis M.

Practical Example 2

FIG. 7 is a ray diagram schematically showing the whole of a projectorsystem 100B according to Practical Example 2. FIG. 8 is a ray diagram ofthe projection optical system 3 of the projector 1 and an attachmentoptical system 10B. FIG. 9 is a configuration diagram of the attachmentoptical system 10B.

As shown in FIG. 7, the projector system 100B in the present example asPractical Example 2 is constituted by the projector 1, and theattachment optical system 10B detachably attached to the projectionoptical system 3 of the projector 1. When the attachment optical system10B is attached to the projector 1, the second optical axis M of theattachment optical system 10B is located on the extension of the firstoptical axis N of the projection optical system 3. An imaging plane ofan optical system of the projector system 100B constituted by theprojection optical system 3 and the attachment optical system 10B is aplane perpendicular to the first optical axis N of the projectionoptical system 3. An imaging plane of an optical system of the projectorsystem 100B, namely an imaging plane of the attachment optical system10B, has a shape of an inside surface of a spherical portion obtained bydividing a sphere. In the present example, the imaging plane of theattachment optical system 10B also has a shape of an inside surface of aspherical portion obtained by dividing a sphere into four equal parts.In the present example, the projector 1 is the same as in PracticalExample 1.

As shown in FIG. 8, the attachment optical system 103 is provided withthe anterior group 11 and the posterior group 12 (the lens groups) . Inthe present example, the anterior group 11 is formed of a single opticalelement 21. The posterior group 12 is provided with a positive lens 32(a second lens), and a negative lens 33 (a third lens) in this orderfrom the demagnification side toward the magnification side. Thepositive lens 32 and the negative lens 33 are disposed at the projectionoptical system 3 side of the optical element 21. The positive lens 32has positive power. The negative lens 33 is disposed at themagnification side of the positive lens 32, and has negative power. Thepositive lens 32 and the negative lens 33 are different in Abbe numberfrom each other. In the present example, the positive lens 32 and thenegative lens 33 are bonded to each other to form a single cemented lens34.

As shown in FIG. 9, the optical element 21 is provided with the plane ofincidence 41 which transmits light from the cemented lens 34, the firstreflecting surface 42 which reflects the light transmitted through theplane of incidence 41, the second reflecting surface 43 which reflectsthe light from the first reflecting surface 42, and the exit surface 44which transmits the light from the second reflecting surface 43. Inother words, the optical element 21 has the plane of incidence 41, thefirst reflecting surface 42 which reflects the light emitted from theplane of incidence 41, the second reflecting surface 43 which reflectsthe light reflected toy the first reflecting surface 42, and the exitsurface 44 which transmits the light reflected by the second reflectingsurface 43. The plane of incidence 41, the first reflecting surface 42,the second reflecting surface 43, and the exit surface 44 are eachprovided with the shape rotationally symmetric around the second opticalaxis M. The plane of incidence 41 is located on the second optical axisM. The plane of incidence 41 is provided with the concave shape concavedtoward the Z2 direction. In other words, the plane of incidence 41 hasthe concave shape concaved toward the Z2 direction (the seconddirection) opposite to the Z1 direction (the first direction) in whichthe projection optical system 3 is located with respect to the opticalelement 21 in an optical axis direction along the second optical axis M.The first reflecting surface 42 is located at the Z2 direction side ofthe plane of incidence 41. Further, the first reflecting surface 42 isdisposed at the Y1 direction side of the second optical axis M. Thefirst reflecting surface 42 is provided with the convex shape convexedtoward the Z1 direction. The second reflecting surface 43 is located atthe Z1 direction side of the first reflecting surface 42. Further, thesecond reflecting surface 43 is disposed at the Y1 direction side of thesecond optical axis M similarly to the first reflecting surface 42. Thesecond reflecting surface 43 is provided with the concave shape concavedtoward the Z1 direction. The exit surface 44 is located at the Z2direction side of the second reflecting surface 43. Further, the exitsurface 44 is disposed at the Y2 direction side of the second opticalaxis M. The exit surface 44 is provided with the convex shape convexedtoward the Z2 direction.

As shown in FIG. 9, the first reflecting surface 42 and the exit surface44 are continuous in the axial light flux pass area (the axial area) 40of the axial light flux passing the second optical axis M in the Ydirection. In other words, the axial light flux pass area 40 is a partof the first reflecting surface 42, and at the same time, a part of theexit surface 44. The axial light flux is the light passing on the firstoptical axis N and the second optical axis M when the attachment opticalsystem 103 is attached to the projector 1. In other words, the axiallight flux pass area 40 is the area of the optical element 21 where thelight passes the first optical axis N and the second optical axis M.Here, the second optical axis M is the design axis of the opticalelement 21. The axial light flux pass area 40 is the area which isuniquely defined when designing the optical element 21.

The first reflecting surface 42 is formed by disposing the reflectivecoating layer on the outside surface at the Z2 direction side of theoptical element 21. In the first reflecting surface 42, the portionoverlapping the axial light flux pass area 40 is provided with thehalf-mirror coating layer as the reflective coating layer. Thus, thelight proceeding on the second optical axis X toward the 22 direction ismade to reach the screen S2. Further, the first reflecting surface 42,the second reflecting surface 43, and the exit surface 44 overlap theplane of incidence 41 in the portion at the side close to the secondoptical axis X when viewed from the Z direction. In the secondreflecting surface 43, the first reflecting part 431 which does notoverlap the plane of incidence 41 when viewed from the Z direction isformed by disposing the reflective coating layer on the outside surfaceat the Z1 direction side of the optical element 21. In the secondreflecting surface 43, the second reflecting part 432 which overlaps theplane of incidence 41 when viewed from the Z direction is formed byproviding the half-mirror coating layer which transmits light proceedingtoward the Z2 direction, and reflects light proceeding toward the Z1direction as the reflective coating layer.

Here, inside the optical element 21, there is formed the intermediateimage 20 which is conjugate with the enlarged image projected on theimaging plane. The intermediate image 20 is also conjugate with theprojection image formed on the demagnification side imaging plane of theprojection optical system 3. In the present example, the intermediateimage 20 is formed between the second reflecting surface 43 and the exitsurface 44.

Lens Data

The numerical aperture of the optical system of the projector system100B constituted by the projection optical system 3 and the attachmentoptical system 10B is 0.291. The lens data of such an optical system isas follows. The surface numbers are provided in sequence from thedemagnification side toward the magnification side. The symbolsrepresent the symbols of the liquid crystal panel, the prism, thelenses, the positive lens, the negative lens, the first transmissivesurface, the first reflecting surface, the second reflecting surface,the second transmissive surface, and the screen. Data of the surfacenumber which corresponds to none of the liquid crystal panel, the prism,the lenses, the positive lens, the negative lens, the first transmissivesurface, the first reflecting surface/the second reflecting surface, thesecond transmissive surface, and the screen is dummy data. The referencesymbol R represents a curvature radius. The reference symbol Drepresents an axial surface distance. The reference symbol C representsan aperture radius. The units of R, D, and C are millimeter. It shouldbe noted that the integer portion of the numerical number shown in theglass material column represents a value obtained by multiplying therefractive index by 10 to the sixth power, and the fractional portionthereof represents a value obtained by multiplying the Abbe number by 10to the second power.

Surface Refraction/ Symbol number Shape R D Glass material Reflection C 2 0 Sphere Infinite 0.0010 Refraction 0.0000  5 1 Sphere Infinite29.9441 BSC7_HOYA Refraction 11.0003 2 Sphere Infinite 10.7129Refraction 16.1307 3 Sphere Infinite 1.3170 Refraction 18.9729 L1 4Sphere 100.7098 5.4431 713667.2948 Refaction 18.8463 5 Sphere −102.11540.1500 Refraction 19.9390 L2 6 Sphere 43.1770 6.7243 643138.5620Refraction 19.6870 7 Sphere −398.2098 14.3689 Refraction 19.3609 L3 8Sphere 25.7153 7.0237 487490.7041 Refraction 12.0000 L4 9 Sphere−26.9720 1.0000 755201.2758 Refraction 11.4463 10 Sphere 22.7296 7.0498Refraction 10.1942 L5 11 Aspheric surface −12.8094 2.0000 ‘D-ZF10_K’Refraction 10.2226 12 Aspheric surface −23.2033 0.2735 Refraction11.0391 L6 13 Sphere 33.2589 2.0000 750866.3234 Refraction 12.3328 L7 14Sphere 21.4173 8.9545 487490.7041 Refraction 12.5458 15 Sphere −32.315417.4196 Refraction 13.0465 L8 16 Sphere 457.3045 8.8399 749259.3458Refraction 16.0000 17 Sphere −40.7661 4.0868 Refraction 16.7967 L9 18Sphere 38.3424 9.0000 743972.4485 Refraction 16.2071 19 Sphere 52.10889.1700 Refraction 14.5342 L10 20 Sphere −24.1062 1.0000 504633.6129Refraction 14.0641 21 Sphere 34.0901 3.0358 Refraction 15.2438 L11 22Aspheric surface 35.8481 4.3495 ‘Z-E48R’ Refraction 16.1241 23 Asphericsurface 34.7555 0.1106 Refraction 17.0742 24 Sphere Infinite 2.8323Refraction 15.8215 32 25 Sphere 43.7364 16.0000 743972.4485 Refraction18.4063 33 26 Sphere −31.0380 14.0000 655261.3319 Refraction 18.3243 27Sphere 48.6756 11.2070 Refraction 18.6311 41 28 Aspheric surface−54.4874 100.0000 ‘Z-330R’ Refraction 18.5177 42 29 Aspheric surface223.2230 −100.0000 ‘Z-330R’ Reflection 63.3811 43 30 Aspheric surface103.6949 100.0000 ‘Z-330R’ Reflection 105.9951 44 31 Aspheric surface−27.7762 10.0000 Refraction 26.5136 32 Sphere Infinite 2768.0000Refraction 1781.1106 S 33 Sphere −2,768.0000 0.0000 Refraction 2906.3556

Aspheric coefficients are as follows.

Surface number S11 S12 S22 S23 R −12.8094 −23.2033 35.8481 34.7555 K 0 0−0.007858933 −8.273411949 A 1.97478E−04 1.50407E−04 −4.73415E−05 −3.44381E−05  B −8.21635E−07  −7.62802E−07  1.11583E−07 7.17727E−08 C8.67659E−09 5.19871E−09 −1.60660E−10  −1.26152E−10  D −2.93527E−11 −2.35712E−11  1.88569E−13 1.10885E−13 E −3.30348E−14  4.53875E−14−1.74526E−16  −3.42914E−17  F 7.83942E−16 2.61603E−19 −1.13308E−20 Surface number S28 S29 S30 S31 R −54.4874 223.2230 103.6949 −27.7762 K6.310243724 −53.5848539 −0.067701944 0.2099999992 A −5.18277E−063.89713E−07 1.60601E−07 −3.91584E−06  B −6.74401E−09 −1.00892E−10 −4.18496E−11  3.56467E−08 C −8.72598E−12 1.14220E−14 4.57110E−15−1.20957E−10  D −2.11538E−19  1.98212E−13 E −1.24378E−16 

The Abbe numbers vd of the positive lens 32 and the negative lens 33 areas follows.

Symbol Surface number νd 32 25 44.85 33 26 33.19

Functions and Advantages

According to the projector system 100B in the present example, it ispossible to obtain substantially the same advantages as those of theprojector system 100A described above.

Further, in the present example, the attachment optical system 10B hasthe posterior group 12 which is disposed at the Z1 direction side of theoptical element 21, and is provided with the positive power. Therefore,it is possible to improve the imaging performance of the attachmentoptical system 10B.

Further, the positive lens 32 and the negative lens 33 constituting theposterior group 12 are different in Abbe number from each other.Therefore, according to the projector system 100B in the presentexample, it becomes easy to correct a chromatic aberration.

FIG. 10 is a diagram showing an MTF at the magnification side of theprojector system 100B. In FIG. 10, the horizontal axis represents aspatial frequency, and the vertical axis represents a contrastreproduction rate. As shown in FIG. 10, the projector system 100B in thepresent example has high resolution.

What is claimed is:
 1. An attachment optical system to detachably beattached to a magnification side of a projection optical system providedto a projection display device, and configured to project projectionlight emitted from the projection optical system on an imaging planedifferent from a magnification side imaging plane of the projectionoptical system, the attachment optical system comprising: an opticalelement having a second optical axis arranged on an extension of a firstoptical axis of the projection optical system, wherein the opticalelement has a plane of incidence arranged on the second optical axis, afirst reflecting surface configured to reflect light emitted from theplane of incidence, a second reflecting surface configured to reflectlight reflected by the first reflecting surface, and an exit surfaceconfigured to transmit light reflected by the second reflecting surface,and the first reflecting surface and the exit surface are continuous inan axial area where light passes the second optical axis and the firstoptical axis.
 2. The attachment optical system according to claim 1,wherein the imaging plane of the attachment optical system is providedwith a shape of an inside surface of a spherical portion obtained bydividing a sphere.
 3. The attachment optical system according to claim1, wherein the plane of incidence has a concave shape concaved toward asecond direction opposite to a first direction in which the projectionoptical system is located with respect to the optical element in anoptical axis direction along the second optical axis, the firstreflecting surface has a convex shape convexed toward the firstdirection, the second reflecting surface has a concave shape concavedtoward the first direction, and the exit surface has a convex shapeconvexed toward the second direction.
 4. The attachment optical systemaccording to claim 1, wherein an intermediate image conjugate with anenlarged image to be projected on the imaging plane is formed inside theoptical element.
 5. The attachment optical system according to claim 1,further comprising: a first lens which is arranged at the projectionoptical system side of the optical element, and has positive power. 6.The attachment optical system according to claim 1, further comprising:a lens group which is arranged at the projection optical system side ofthe optical element, and has positive power, wherein the lens group hasa second lens having positive power, and a third lens having negativepower, and the second lens and the third lens are different in Abbenumber from each other.
 7. A projection display system comprising: theattachment, optical system according to claim 1; and a projectiondisplay device having a projection optical system, wherein theattachment optical system is detachably attached to the projectionoptical system.
 8. The projection display system according to claim 7,wherein the projection display device includes a light modulationelement configured to modulate light emitted from a light source to forma projection image, the light modulation element is arranged on ademagnification side imaging plane of the projection optical system, andforms the projection image at one side of the first optical axis of theprojection optical system, first projection light emitted from theprojection optical system spreads toward another side of the firstoptical axis, the first reflecting surface and the second reflectingsurface are arranged at another side of the second optical axis, theexit surface is arranged at one side of the second optical axis, andsecond projection light emitted from the attachment optical systemspreads toward one side of the second optical axis.